The ability to cause fast changes in temperatures, particularly between very low temperatures and room or higher temperatures, on a desired surface and at a desired location, is of practical importance in many uses. Fast temperature changes can be exploited, for instance, in the treatment of various materials, for sealing or surface curing purposes, etc.
Cold and hot surfaces are used also for medical uses. For instance, cryogenic techniques are employed to destroy malignant tissues, or for plastic surgery. One example of such a use is presented in SU 774,549, which relates to a thermal treatment of biological tissues by passing heat carriers through a cryosurgical probe. The method is said to be useful in the cryo-surgery of the human brain. This method, however, involves passing a heat carrier through a surgical probe, its subsequent heating and repeated passage through the probe. Acetone or alcohol are used as the heat carrier. Prior to its passage through the probe the heat carrier is either cooled to -70.degree.-75.degree. C., or heated to +70.degree.-90.degree. C.
Devices of this type present severe drawbacks, inasmuch as they have long lags in temperature changes, they require cumbersome heating/cooling apparatus outside the probe, and are complicated and expensive to use.
Cryosurgical instruments having both crycooling and heating capabilities are also known in the art. One such device and its medical use have been described by Andrew A. Gage ["Current Issues in Cryosurgery", Cryobiology 19, 219-222 (1982), at pp. 220.degree.-21]. The device described therein was cooled by liquid nitrogen and electrically heated, to provide hemostasis. The electrical heating, however, by its nature is a relatively slow procedure.
Another device is described in SU 1,217,377, which exploits the expansion of gases through an orifice. However, simple expansion of gas through an orifice provides relatively slow temperature changes, and the changes in temperature are relatively mild. Thus, for instance, in the device of SU 1,217,377 it is not possible to liquify nitrogen. Additionally, this prior art device employs helium at room temperature which, expanding from a pressure of about 300 atmospheres, will attain a heating of merely about 30.degree. C. In any case, in the single pass expansion described in this reference, liquefaction of nitrogen cannot be achieved. However, helium has an inversion temperature of about 45 K., which renders it possible to employ neon or hydrogen as the second gas, as is done in this reference. The highest inversion temperature of neon is about 200 K., and of hydrogen is about 180 K. Accordingly, these gases cannot be used while using nitrogen as the first gas, because the temperature of liquid nitrogen is 80 K., and thus the heating obtainable with neon and hydrogen is low. Additionally, neon and hydrogen may be found at an inversion temperature lower than their maximal temperature, so that no heating is obtained. However, neon is expensive and hydrogen is dangerous, and the obtainable temperatures are unsatisfactory for many uses, which accounts for the lack of success of the above-mentioned device.
Prior art devices and methods have so far failed to provide simple and effective fast temperature changing means which can be used in order to exploit the potential of cryogenic techniques, in industry and in medicine. It is therefore clear that it would be highly desirable to be able to exploit such methods in as many as possible applications.